Dynamic resonant circuits for chemical and physical sensing with a reader and RFID tags

ABSTRACT

A tag for detecting an analyte can include a radio frequency identification tag including a sensor portion, the sensor portion configured to change resistivity when the radio frequency identification tag contacts or interacts with an analyte, whereby the resistivity change alters an output of the radio frequency identification tag, wherein the sensor portion includes a circuit, and wherein the sensor portion is configured to activate the circuit or deactivate the circuit when contacted or having interacted with the analyte, where the sensor portion includes a plurality of carbon nanotubes associated with a chemically-degradable polymer. In certain embodiments, the chemically degradable polymer can be a metallo-supramolecular polymer.

PRIORITY CLAIM

This application is a divisional of U.S. application Ser. No.15/453,217, filed on Mar. 8, 2017, which claims the benefit of U.S.Provisional Application No. 62/305,360 filed on Mar. 8, 2016, each ofwhich is incorporated by reference in its entirety.

This application claims the benefit of U.S. Provisional Application No.62/305,360 filed on Mar. 8, 2016, which is incorporated by reference inits entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Grant No.DMR1410718 awarded by the National Science Foundation and under ContractNo. W911NF-13-D-0001 awarded by the Army Research Office. The Governmenthas certain rights in the invention.

TECHNICAL FIELD

This invention relates to wireless sensing.

BACKGROUND

Chemical sensors offer opportunities for improving personal security,safety, and health. To enable broad adoption of chemical sensorsrequires performance and cost advantages that are best realized frominnovations in the design of the sensing (transduction) materials. Idealmaterials are sensitive and selective to specific chemicals or chemicalclasses and provide a signal that is readily interfaced with portableelectronic devices. Traditional solutions suffer from limitations, suchas being expensive, bulky, or fragile, or requiring of trained personnelto operate. In addition, many traditional methods of sensing requirephysical contact of the device with the sensing element/material viawires or solid-state circuitry to acquire data.

SUMMARY

In one aspect, a tag for detecting an analyte can include a radiofrequency identification tag including a sensor portion, the sensorportion configured to change resistivity when the radio frequencyidentification tag contacts or interacts with an analyte, whereby theresistivity change alters an output of the radio frequencyidentification tag, wherein the sensor portion includes a circuit, andwherein the sensor portion is configured to activate the circuit ordeactivate the circuit when contacted or having interacted with theanalyte, where the sensor portion includes a conductive materialassociated with a chemically-degradable polymer.

In certain embodiments, the conductive material can include carbonnanotubes.

In certain embodiments, the chemically-degradable polymer can include aligand and a metal ion.

In certain embodiments, the polymer can be a supramolecular polymer.

In certain embodiments, the carbon nanotubes and thechemically-degradable polymer can form a porous network.

In certain embodiments, the polymer can be a polycyclic aromaticpolymer.

In certain embodiments, the polymer can include a polarizable πelectron.

In certain embodiments, the polymer can include an anthracene-basedligand.

In certain embodiments, the polymer and the metal can form a squaremetal structure.

In certain embodiments, the metal ion can be Cu²⁺ or Ni²⁺.

In certain embodiments, the conductive material can include graphene.

In certain embodiments, the conductive material can include metaloxides.

In certain embodiments, the conductive material can include ametal-organic-framework.

In certain embodiments, the analyte can be a nerve agent.

In certain embodiments, the analyte can be a strong electrophile.

In certain embodiments, the analyte can be diethylchlorophosphate orthionyl chloride.

In certain embodiments, an amount of the plurality of carbon nanotubesand an amount of the polymer can be 1:1.

In certain embodiments, each of the plurality of the carbon nanotubescan be wrapped by the polymer.

In certain embodiments, the radio frequency identification tag can be anear-field communication tag.

In certain embodiments, the tag can be incorporated into a badge capableof being worn by a person.

A system for detecting an analyte can include a radio frequencyidentification tag including a sensor portion, the sensor portionconfigured to change resistivity when the radio frequency identificationtag contacts or interacts with an analyte, whereby the resistivitychange alters an output of the radio frequency identification tag,wherein the sensor portion includes a circuit, and wherein the sensorportion is configured to activate the circuit or deactivate the circuitwhen contacted or having interacted with the analyte, where the sensorportion includes a plurality of carbon nanotubes associated with achemically-degradable polymer and a detector.

In certain embodiments, the detector can be a reader.

In certain embodiments, the reader can be a hand held reader.

In certain embodiments, a hand held reader can be a smartphone.

In certain embodiments, the tag can become readable from unreadable tothe detector after the conductivity changes.

In certain embodiments, the tag can become unreadable from readable tothe detector after the conductivity changes.

In certain embodiments, the system can include a dosimeter.

In certain embodiments, the dosimeter can be a radiation dosimeter, achemical warfare agent dosimeter, a volatile organic compound dosimeter,or an analyte dosimeter.

In certain embodiments, the system can monitor a pollutant, a chemicalrelevant to occupational safety, a nerve agent, or a pulmonary agent.

In certain embodiments, the system can include a plurality of tags.

In certain embodiments, each of the plurality of tags can be capable ofdetecting at least one analyte.

In another aspect, a method of detecting an analyte can includedetecting an output from a radio frequency identification tag includinga sensor portion, the sensor portion configured to change resistivitywhen the radio frequency identification tag contacts or interacts withan analyte, whereby the resistivity change alters an output of the radiofrequency identification tag, wherein the sensor portion includes acircuit, and wherein the sensor portion is configured to activate thecircuit or deactivate the circuit when contacted or having interactedwith the analyte, where the sensor portion includes a plurality ofcarbon nanotubes associated with a chemically-degradable polymer.

In certain embodiments, the method can further include detecting theoutput of the radio frequency identification by a reader.

In certain embodiments, the reader can include a hand-held, mobileplatform, or stationary reader.

In certain embodiments, the reader can include a smartphone.

In certain embodiments, the output can be detectable by a reader afterthe output is shifted by detection of the analyte.

In certain embodiments, the output can be detectable by a reader afterthe output going through a physical object.

In certain embodiments, the analyte can contact or interact with aportion of the surface of the radio frequency identification tag.

In certain embodiments, the sensor portion can be located on a portionof a surface of the radio frequency identification tag.

In certain embodiments, the sensor portion can be surrounded by anantenna coil.

In certain embodiments, the sensor portion can have a surface area lessthan the surface area of the radio frequency identification tag.

In certain embodiments, the radio frequency identification tag may notrequire a power source.

In certain embodiments, the method can further include altering anelectrical connection within the radio frequency identification tag.

In certain embodiments, the sensor portion can include multiple sensinglocations.

In another aspect, a method of making a tag can include making adispersion with a conductive material associated with achemically-degradable polymer and a solvent and drop-casting thedispersion on a substrate.

In certain embodiments, the conductive material can include carbonnanotubes.

In certain embodiments, the chemically-degradable polymer can include aligand and a metal ion.

In certain embodiments, the polymer can be a supramolecular polymer.

In certain embodiments, the carbon nanotubes and thechemically-degradable polymer can form a porous network.

In certain embodiments, the polymer can be a polycyclic aromaticpolymer.

In certain embodiments, the polymer can include a polarizable πelectron.

In certain embodiments, the polymer can include an anthracene-basedligand.

In certain embodiments, the polymer and the metal can form a squaremetal structure.

In certain embodiments, the metal ion can be Cu²⁺ or Ni²⁺.

In certain embodiments, the solvent can include a dichlorobenzene (DCB).

In certain embodiments, the solvent can further include toluene.

In certain embodiments, a ratio of DCB to toluene can be 1:4.

In certain embodiments, the method can further include centrifuging thedispersion and taking a supernant of the dispersion for drop-casting.

Other aspects, embodiments, and features will be apparent from thefollowing description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D show formation of metallo-supramolecular polymers (MSPs).FIG. 1A shows chemical structures of AL and MSP. FIGS. 1B and 1C showUV-Vis titration experiments of AL with Cu(AcO)₂.H₂O at roomtemperature. FIG. 1D shows an STM image of MSP(Cu) assembled onhighly-oriented pyrolytic graphite (HOPG).

FIGS. 2A-2C show dispersion of SWCNT with MSPs. FIG. 2A shows scheme fordispersing SWCNT with MSPs. FIG. 2B shows UV-Vis-NIR spectra of SWCNTdispersed by MSP(Cu) and MSP(Ni) in o-DCB. FIG. 2C shows an SEM image ofa drop-cast film of SWCNT/MSP(Cu) on Si substrate.

FIGS. 3A-3C show chemical sensing properties of SWCNT wrapped with MSP.FIG. 3A shows configuration of SWCNT-based chemiresistive sensor. FIG.3B shows conductance traces of SWCNT-based chemiresistive sensors uponexposure to DECP. FIG. 3C shows chemiresisitve responses of SWCNT-basedchemiresistive sensors upon exposure to various vapors in N₂.

FIGS. 4A-4C show monitoring of trace DECP using optimized SWCNT/MSP(Cu)sensors. FIG. 4A shows conductance traces of optimized SWCNT/MSP(Cu)chemiresistive sensors upon exposure to various concentrations of DECPin N₂. FIG. 4B shows chemical structures of ALOx and pralidoxime. FIG.4C shows conductance traces of optimized SWCNT/MSP(Cu) chemiresistivesensors made from 0.5:0.5:1.0 (by mole) mixtures of ALOx, AL, and Cu²⁺upon exposure to various concentrations of DECP in N₂.

FIG. 5 shows modification of NFC tag and smart phone detection ofthionyl chloride in air.

FIG. 6 shows schematic of insulated network and conductive network.

FIG. 7 shows synthetic route of AL and ALOx.

FIG. 8 shows ¹H-NMR spectrum of 2,6-dimethoxy-9,10-dioctyl-anthracene.

FIG. 9 shows ¹³C-NMR spectrum of 2,6-dimethoxy-9,10-dioctyl-anthracene.

FIG. 10 shows ¹H-NMR spectrum of crude product of2,6-dibromo-3,7-dimethoxy-9,10-dioctyl-anthracene.

FIG. 11 shows ¹H-NMR spectrum of3,7-dimethoxy-9,10-dioctyl-anthracene-2,6-dicarbaldehyde.

FIG. 12 shows ¹³C-NMR spectrum of3,7-dimethoxy-9,10-dioctyl-anthracene-2,6-dicarbaldehyde.

FIG. 13 shows ¹H-NMR spectrum of3,7-dihydroxy-9,10-dioctyl-anthracene-2,6-dicarbaldehyde.

FIG. 14 shows ¹³C-NMR spectrum of3,7-dihydroxy-9,10-dioctyl-anthracene-2,6-dicarbaldehyde.

FIG. 15 shows ¹H-NMR spectrum of9,10-dioctyl-3,7-bis-propyliminomethyl-anthracene-2,6-diol (AL).

FIG. 16 shows ¹³C-NMR spectrum of AL.

FIG. 17 shows ¹H-NMR spectrum of3,7-dihydroxy-9,10-dioctyl-anthracene-2,6-dicarbaldehyde dioxime (ALOx).

FIG. 18 shows ¹³C-NMR spectrum of ALOx.

FIG. 19 shows ¹H-NMR spectrum ofpoly-(9,9-di-(2′-ethylhexyl)-2,7-dibromofluorene) FIG. 20 showstitration of AL with Ni²⁺.

FIG. 21A shows chemical structures of compounds used for gel permeationchromatography (GPC) experiments. FIG. 21B shows GPC experiments for themixtures of AL and PFO. FIG. 21C shows GPC experiments for the mixturesof MSP(Cu), PFO, and OxP.

FIG. 22A shows dispersion of SWCNT by metal ligand complexes of AL. FIG.22B shows chemiresistive response of SWCNT+MSP sensors upon exposure tosaturated acetyl chloride.

FIG. 23A shows mixture of SWCNT by DSA(Ni) in o-DCB after sonication.FIG. 23B shows chemiresistive response of SWCNT mixed with DSA(Ni) uponexposure to saturated DMCP.

FIG. 24 shows an SEM image of pristine SWCNT.

FIG. 25 shows chemiresistive response of SWCNT+MSP(Cu) sensors uponexposure to saturated DMCP.

FIG. 26 shows chemiresistive response of SWCNT+MSP(Cu) sensors uponexposure to saturated DMCP.

FIG. 27A shows chemiresistive response of SWCNT+MSP(Cu) sensors uponexposure to saturated DMCP. FIG. 27B shows chemiresistive response ofSWCNT+MSP(Cu) sensors after applying centrifuge.

FIG. 28A shows UV-Vis-NIR spectra of SWCNT+MSP(Cu) dispersed by o-DCBand toluene mixtures. FIG. 28B shows UV-Vis-NIR spectra of AL andMSP(Cu) in o-DCB.

FIG. 29A shows chemiresisitive response of SWCNT+MSP (prepared in o-DCB)for trifluoroacetic acid. FIG. 29B shows chemiresisitive response ofSWCNT+MSP(Cu) (prepared in o-DCB:Toluene=1:4, non centrifuged) forthionyl chloride.

FIG. 30A shows ¹H-NMR spectra of DSA(Ni) in CDCl₃ before and afterbubbling with DMCP vapor in dry Ar. For comparison, ¹H-NMR spectra ofDSA and DMCP are also shown. FIG. 30B shows ¹H-NMR spectra of DSA(Ni) inCDCl₃ before and after addition of 0.5 molar equivalent of acetylchloride. For comparison, ¹H-NMIR spectra of free DSA and acetylester ofDSA are also shown.

FIGS. 31A-31C show additional evidences of demetallation of MSP(Cu) withelectrophiles. FIG. 31A shows MALDI-TOF-MS spectra of SWCNT+MSP(Cu)before and after exposure to DMCP. FIG. 31B shows UV-Vis-NIR spectra ofSWCNT+MSP(Cu) film on quartz before and after exposure to DMCP. FIG. 31Cshows IR spectra of DSA(Ni) in CCl₄ before and after bubbling with DMCPvapor.

FIG. 32 shows precipitation of SWCNT+MSP(Cu) dispersion in o-DCBimmediately after bubbling the dispersion with DMCP.

FIGS. 33A-33B show UV-Vis titration experiments of ALOx (7.0×10⁻⁵ M,o-DCB/methanol=9/1) with Cu(AcO)₂.H₂O (10.6 mM, methanol) at roomtemperature. The optical path length was 10 mm. Note that aggregationwas observed upon addition of Cu²⁺.

FIGS. 34A-34B show baseline correction data for 0.1 ppm DECP sensing.FIG. 34A shows conductance traces of optimized SWCNT/MSP(Cu)chemiresistive sensors made from 1:1 mixtures of AL and Cu²⁺ (in mole)upon exposure to DECP in N₂. FIG. 34B shows conductance traces ofoptimized SWCNT/MSP(Cu) chemiresistive sensors made from 0.5:0.5:1.0mixtures of ALOx, AL, and Cu²⁺ (in mole) upon exposure to DECP in N₂.

FIG. 35A shows circuit design of an NFC tag. FIGS. 35B-35C shows aresonance spectrum of modified NFC tag for design of turn-on sensor.

FIG. 36 shows experimental set up for monitoring of conductivity ofsensing materials.

DETAILED DESCRIPTION

Development of portable and low-cost technologies for chemical andphysical sensing is important for human health, safety, and quality oflife. Such systems can be used for point-of-care diagnosis of disease,detection of explosives and chemical warfare agents, prevention ofspoilage of food and increasing efficiency in agriculture, analysis ofoil and gas, detection of petrochemical leaks and spills, monitoring ofenvironmental pollution, detection of radiation, and monitoring oftemperature or heat energy exposure. Traditional improvements in thisarea increase performance through modification or re-engineering ofexisting platforms. Such strategies may include miniaturizing componentsto increase portability (e.g., portable gas chromatograph or massspectrometer) or reducing cost (e.g., increasing the efficiency of themanufacturing). While these solutions may improve existing platforms interms of portability, they still suffer from limitations, such as beingexpensive, bulky, or fragile, or requiring of trained personnel tooperate. Furthermore, many traditional methods of chemical sensingrequire physical contact of the device with the sensing element/materialvia wires or solid-state circuitry to acquire data.

Low cost and portable chemical sensors facilitate personal monitoringand sharing information of hazardous chemical substances (e.g., toxicgases, explosives, and carcinogens), which are of increasing interestfor security, occupational safety, and health. See, Taylor, R. F.;Schultz, J. S. Handbook of Chemical and Biological Sensors (IOPPublishing, 1996), and Korotcenkov, G. Handbook of Gas Sensor Materials:Properties, Advantages and Shortcomings for Applications Volume 2: NewTrends and Technologies (Springer, 2007), each of which is incorporatedby reference in its entirety. Chemiresistive sensors are attractivedevices to realize distributed low cost sensors and operate on a simplevariation of electrical conductivity of sensing materials in response toanalytes of interest. See Neri, G. Chemosensors 2015, 3, 1-20, which isincorporated by reference in its entirety. The direct electrical natureof the transduction in these devices is ideal for integration intoomnipresent electronic devices. Various types of conductive materials(e.g., carbon, metal oxides, and metal-organic-frameworks) can beemployed in chemiresistive sensors. See, Neri, G. Chemosensors 2015,3,1-20, and Campbell; M. G., Sheberla, D.; Liu, S. F.; Swager, T. M.;Dinc{hacek over (a)}a, M. Angew. Chem. Int. Ed. 2015, 54, 4349-4352,each of which is incorporated by reference in its entirety.Semiconductive single walled carbon nanotubes (SWCNT) are particularlyinteresting as a result of their high chemical and thermal stability,relatively small responses to humidity, and compatibility withsolvent-mediated processes. See, Kauffman, D. R.; Star, A. Angew. Chem.Int. Ed. 2008, 47, 6550-6570, Snow, E. S.; Perkins, F. K.; Robinson, J.A. Chem. Soc. Rev. 2006, 35, 790-798, Schnorr, J. M.; Swager, T. M.Chem. Mater. 2011, 23, 646-657, and Fennell, J. F., Jr.; Liu, S. F.;Azzarelli, J. M.; Weis, J. G.; Rochat, S.; Mirica, K. A.; Ravnsbæk, J.B.; Swager, T. M. Angew. Chem. Int. Ed. 2016, 55, 1266-1281, each ofwhich is incorporated by reference in its entirety. SWCNTs do notpossess intrinsic selectivity for specific target analyte molecules andhence a major element of creating useful sensors from these materialsinvolves functionalization with chemical units that enable selectiveresponses to molecules or classes of reactive compounds. Chemicalselectivity is commonly imparted upon SWCNTs by covalent attachment ofselectors or receptors, resulting in robust chemiresistor stability.However, reactive functionalization of graphene surfaces disruptsπ-system, thereby negatively impacting sensitivity by limiting thedynamic range of the resisitivity. Conversely, non-covalentfunctionalization methods are less perturbative to the π-electronicstructure of SWCNTs. See Fujigaya, T.; Nakashima, N. Sci. Tech. Adv.Mater. 2015, 16, 024802, which is incorporated by reference in itsentirety. Modification of SWCNTs ideally enhance a chemiresistiveresponses (defined as (G₁-G₀)/G₀×100(%), where G₀ and G₁ are initial andmeasured conductance) to target analytes relative to other chemicals inthe surroundings. A central goal is to develop methods that increasechemiresistive responses to target analytes relative background noise,and this need is particularly important when the target analytes aretoxic at trace (parts per million or lower) concentrations. See Romano,J. A., Jr.; Lukey, B. J.; Salem, H. Chemical Warfare Agents: Chemistry,Pharmacology, Toxicology, and Therapeutics, Second Edition (CRC Press,2007), which is incorporated by reference in its entirety.

The cumulative exposure of toxic chemicals at trace concentrations isoften of interest, and chemical dosimeters offer an important means forquantifying these events. Physical dosimeters from multi-walled carbonnanotubes wrapped with insulating poly(olefin sulfone)s display largeincreases in conductivity (ca. 10,000%) by radiation-induced degradationof the resistive polymer wrapper to create direct MWCNT-MWCNT contacts.See, Lobez, J. M.; Swager, T. M. Angew. Chem. Int. Ed. 2010, 49, 95-98,which is incorporated by reference in its entirety. In this case,evaporation of degradation products of poly(olefin sulfone)s (as SO₂ andolefin) is critical for promoting direct MWCNT-MWCNT contacts. Althougha limited number of synthetic polymers produce volatile degradationproducts, this concept has the potential for general utility to createchemiresistive dosimeters.

Examples of Some Sensors

One method of detecting an analyte in a sample includes a carbon-carbonmultiple bond moiety comprising exposing a detection region of adetector including a heteroaromatic compound having an extrudable groupand capable of undergoing Diels-Alder reaction with the analyteincluding a carbon-carbon multiple bond moiety to the sample, anddetecting color change of a reaction mixture comprising theheteroaromatic compound based on the presence of the analyte in thesample. This method provides alkene and alkyne detection,differentiation, and quantitation that addresses the growing need oftransducing relevant information (only previously attainable fromsophisticated methods such as GC-analysis) with the favorable low-costand ease-of-use attributes ascribed to more basic technologies. Usingthis method, a device can indicate the presence of specific classes ofalkenes or alkynes in the gas phase, and can determine the totalexposure of the device to said alkenes or alkynes, based on acolorimetric readout. Because this device is selective for certainclasses of alkenes and alkynes, it allows for differentiation ofcompounds of interest that contain certain alkene or alkynefunctionality. This method can make use of the color change thataccompanies the transformation of an s-tetrazine moiety to a pyrimidinemoiety upon reaction with unsaturated carbon-carbon bonds. See, forexample, Application No. PCT/US2014/033037, which is incorporated byreference in its entirety.

Another method of detecting a stimulus includes using a dosimeter, suchas a thermal dosimeter, which can measure the amount of light emittedfrom a crystal in a detector when the crystal is heated. A dosimeter canuse a triazole as described by Coulembier. See, for example, O.Coulembier et al., Macromolecules, 2006, 39, 5617-5628, which isincorporated by reference in its entirety.

Sensors Using a Digital Reader

Sensing platforms that have the characteristics of being simple,inexpensive, yet sensitive and quantitative can be created. One approachto the area of chemical and physical sensing can be the development ofsensing materials and devices that have the characteristics of beingmodular (i.e., easily modified for specific applications), wirelesslyreadable, and easily used and interpreted by individuals with no priortechnical training.

Whitesides and co-workers have demonstrated chemical detection ofanalytes in biologically-relevant samples using smartphones. See, forexample, Martinez, A. W. et al., Anal. Chem., 2008, 80, 3699-3707, whichis incorporated by reference in its entirety. These methods involvecapturing an image of a colorimetric assay using an in-phone camera andanalyzing it to correlate changes in color of a dye with the presence ofbiologically relevant analyte. This method, however, requiresline-of-sight measurement that can be affected by potential artifactsarising from lighting conditions, positional angle, or hand-movementduring image acquisition.

Potyrailo et al. and others demonstrated electronic wireless detectionof chemical analytes using RFID technology. See, for example, Potyrailo,R. A. et al., Anal. Chem. 2006, 79, 45-51, which is incorporated byreference in its entirety. While this technology has the capability toperform non-line-of sight measurements that overcome some of thelimitations of the colorimetric assays, they have limited portability asthey require the use of advanced electronics devices, such asinductively coupled network analyzers or impedance spectrometers.

Studies have exploited custom-made, as well as commercially availableRFID tags to monitor freshness of milk, freshness of fish, and growth ofbacteria. See, for example, Tao, H. et al., Adv. Mater. 2012, 24,1067-72; Potyrailo, R. A. et al., Battery-free Radio FrequencyIdentification (RFID) Sensors for Food Quality and Safety, 2012, each ofwhich is incorporated by reference in its entirety. These studies reliedprimarily on correlating the changes in dielectric environment of theRFID tags (i.e., changes in C) with changes in the resonant frequency orresonant impedance of the LCR circuit. However, they are limited by alack of selectivity toward chemical analytes and physical stimuli, andby the requirement for expensive radio frequency analysis equipment suchas impedance and network analyzers for chemical detection.

Although RF technology has been recently applied towards wirelesschemical sensing, current approaches have several limitations includinglack of specificity to selected chemical analytes, requirements forexpensive, bulky, fragile, and operationally complex impedance andnetwork analyzers, and reliance on extensive data processing andanalysis. See, Potyrailo R A, Surman C, Nagraj N, Burns A (2011)Materials and transducers toward selective wireless gas sensing. ChemRev 111:7315-7354, Lee H et al. (2011) Carbon-nanotube loadedantenna-based ammonia gas sensor. Microw Theory Tech IEEE Trans59:2665-2673, Potyrailo R A et al. (2009) Development of radio-frequencyidentification sensors based on organic electronic sensing materials forselective detection of toxic vapors. J Appl Phys 106:124902, Fiddes L K,Yan N (2013) RFID tags for wireless electrochemical detection ofvolatile chemicals. Sensors Actuators B Chem 186:817-823, Fiddes L K,Chang J, Yan N (2014) Electrochemical detection of biogenic aminesduring food spoilage using an integrated sensing RFID tag. SensorsActuators B Chem 202:1298-1304, Occhiuzzi C, Rida a., Marrocco G,Tentzeris M M (2011) Passive ammonia sensor: RFID tag integrating carbonnanotubes. 2011 IEEE Int Symp Antennas Propag: 1413-1416, each of whichis incorporated by reference in its entirety.

A commercially available technology—Near Field Communication (NFC)—canbe used for wireless, non-line-of-sight chemical sensing. Many modernsmartphones and similar devices (tablet computers, video gamecontrollers, and smartphone accessories) can be equipped with NFCreaders operating at peak frequency of 13.56 MHz. These readers can betuned to interact with many types of commercially available wireless“tags”—simple electrical circuits comprising an inductor (L), acapacitor (C), and an integrated circuit (resistor (R)) supported on thesurface of a substrate, such as a polymeric sheet. The phone can achievecommunication by powering the tag via electromagnetic induction at thespecified frequency and then receiving reflected attenuated signal backfrom the tag. See, for example, Curty, J. P. et al., Springer, New York,2007, pp. 49-73, which is incorporated by reference in its entirety.This technology can be used in controlling access to facilities,ticketing of events, prevention of theft, and management of inventory.This technology can be applied to chemical sensing by introducingchemiresistive materials into the circuitry of the tag. Exposure of themodified tag to chemical vapors can alter the resistance of the sensingmaterials, and thus the resonant frequency of the modified tag, suchthat it becomes readable or unreadable when probed by a smartphonereader. With this method, vapors of nitric acid, ammonium hydroxide andcyclohexanone, can be detected. This technology can be extended tophysical sensors as well, such as applications in temperature, heatenergy exposure or radiation sensing.

Commercially available RFID tags can be combined with a digital reader,such as a hand held frequency reader, for example a consumer electronicsmartphone, resulting in a fully integrated chemical and physicalsensing platform. The sensing platform can be available to anyone,including those without a technical background. This platform hasadvantages over existing methods of chemical and physical sensing. Forexample, the sensing method can be non-line-of-sight (high frequencyradio waves), and can receive information from the sensor tag throughsolid objects such as packages, walls, wood, and other non-metallicobjects. The sensing tag does not require a power source, as it receivesits power from the incoming radio waves. The data-acquiring device canbe any commercially available smartphone equipped with near fieldcommunication (NFC) reader capabilities, including but not limited toSamsung, LG, Google, Blackberry, etc. manufacturers. The method issimple: no technical knowledge is required to perform a measurement.

The chemical detection can be achieved using NFC technology instead ofimpedance spectroscopy and the detector can be a highly portable devicesuch as a smartphone, instead of a very bulky complex instrument (e.g.,a network analyzer). Besides portability, the smartphone has additionalutility in chemical detection because the information obtained from thechemical sensor can be coupled with other sensors within the smartphone(e.g., GPS, email) for automated identification of position andcommunication of information. Ability for wireless chemical sensing overdistance of 5 cm of solid material was demonstrated, as opposed tothrough a distance of a single paper sheet. This method incorporateschemiresistors into the existing circuitry of a tag by drawing asopposed to depositing sensing materials on top of the antenna. Thismethod requires no data workup for signal processing, while existingmethods often require substantial amount of data processing forinterpreting information. This method does not require additionalequipment for reading the magnetic memory. This method relies on changeson resistance of a selective chemiresistive or physiresistive materialfor chemical sensing, while existing methods rely on non-specificchanges in capacitance. This method relies on molecular recognition forselectivity, and does not require principal component analysis, and soon. A nascent technology can be embedded in modern smartphones—NearField Communication (NFC)—for wireless electronic, portable,non-line-of-sight selective detection of gas-phase chemicals.NFC-enabled smartphones communicate with NFC tags by simultaneouslyenergizing the NFC tag with an alternating magnetic field (e.g. f=13.56MHz) through inductive coupling and transferring data by signalmodulation. NFC tags are converted into Chemically Actuated ResonantDevices (CARDs) by disrupting the LCR circuit (Step 1) and recompletingthe circuit with a stimuli-responsive variable circuit component bydrawing (Step 2) with solid sensing materials.

This concept can be demonstrated by (i) incorporating carbon-basedchemiresponsive materials into the electronic circuitry of commercialNFC tags by mechanical drawing, and (ii) using an NFC-enabled smartphoneto relay information regarding the chemical environment (e.g., presenceor absence of a chemical) surrounding the NFC tag. In this way,part-per-million (ppm) concentrations of ammonia and cyclohexanone andpart-per-thousand (ppth) concentrations of hydrogen peroxide can bedetected and differentiated. Wireless acquisition and transduction ofchemical information can be coupled with existing smartphone functions(e.g., GPS).

Many commercial smartphones and mobile devices are equipped with NFChardware configured to communicate wirelessly with NFC “tags”—simpleelectrical resonant circuits comprising inductive (L), capacitive (C),and resistive (R) elements on a plastic substrate (FIG. 18). Thesmartphone, such as the Samsung Galaxy S4 (SGS4), employed in thisstudy, communicates with the battery-free tag by powering its integratedcircuit (IC) via inductive coupling at 13.56 MHz. See, Nitkin P V., RaoK V S, Lazar S (2007) An overview of near field UHF RFID. 2007 IEEE IntConf RFID:167-174, which is incorporated by reference in its entirety.Power transferred from the smartphone to the IC is, among othervariables, a function of the transmission frequency (f), the resonantfrequency (A), the quality factor (Q), and the circuit efficiency (η),which in turn are functions of L (H), C (F), and R (Ω) of the smartphoneand NFC resonant circuit components. See, Jing H C, Wang Y E (2008)Capacity performance of an inductively coupled near field communicationsystem. 2008 IEEE Antennas Propag Soc Int Symp 2:1-4, which isincorporated by reference in its entirety. Integration ofchemiresponsive materials into commercial NFC tags producesstimuli-responsive variable circuit components that affect powertransfer between the tag and a smartphone in the presence or absence ofchemical stimuli. The resulting programmable Chemically ActuatedResonant Devices (CARDs) enable non-line-of-sight smartphone chemicalsensing by disrupting or allowing RF communication.

In one method, commercially available high frequency (HF) radiofrequency identification tags compatible with a reader can be convertedinto chemical and physical sensors. The reader can be a digital reader,which can be a handheld frequency reader. The reader can be portable.The reader can be a smartphone. In parallel with the sensing capability,a smartphone reader can read other things, such as GPS coordinates,acceleration, light intensity, altitude, etc. Coupling thesecapabilities in one portable reader can have unprecedented utility.

This technology can be extended to temperature, heat energy exposure andradiation sensing as well. The modification of the tag can involveintegration of chemiresistive sensing materials by drawing ordropcasting onto the surface of the tag. Depending on the design, thetag can become readable or unreadable when exposed to vapors ofchemicals or physical stimulus.

A stimulus can include an analyte. The stimulus can include a vapor, agas, a liquid, a solid, a temperature change, heat energy exposure andso on. The stimulus can include an ethylene, a mold, an acid, a ketone,a thiol, an amine, and so on. Using RFID, a stimulus can be detected;for example, vapors of nitric acid and cyclohexanone can be detected;and ethylene and mold can be detected; and biological warfare agents canbe detected. Cumulative exposure of analytes can be detected andquantified with a dosimeter.

A stimulus can include a physical stimulus. The physical stimulus caninclude light, heat, or radiation. Using RFID, a stimulus can bedetected for example, exposure of a tag to heat can be detected; andradiation and light can be detected. Cumulative exposure of physicalstimulus can be detected and quantified with an RFID dosimeter.

A sensing material can produce detectable change in resistance and/orcapacitance upon chemical, biological, or physical changes around thesensing device. A property of a sensing material that can change uponexposure to the environment includes, but is not limited to, change incapacitance, change in resistance, change in thickness, change inviscoelasticity, or a combination thereof.

A sensing material can include a metal, an organic material, adielectric material, a semiconductor material, a polymeric material, abiological material, a nanowire, a semiconducting nanoparticle, a carbonnanotube, a carbon nanotube network, a nanofiber, a carbon fiber, acarbon particle, carbon paste, or conducting ink, or combinationthereof.

Different approaches can be taken to introduce chemical and physicalsensing materials. For example, sensing materials can be introduced intotwo different locations within a commercial RFID tags. Sensing materialsinclude variable resistors that alter their resistance in response to astimulus. A stimulus can be a chemical stimulus, a physical stimulus, abiological stimulus, etc. The detection of a stimulus can be achieved byswitching the tag between a “readable” and “not readable” state, byexposure to a stimulus, such as chemical vapors or changes intemperature or heat energy exposure, for example.

When a stimulus contacts or interacts with a sensor, the resistivity canchange. The contact or interaction can produce a readable signal in ahand held frequency reader as a result of the resistivity change.Alternatively, the contact or interaction can turn off a readable signalin a hand held frequency reader as a result of the resistivity change.Output can be detected after the output is shifted by detection of thestimulus. Even after going through a physical object, the output canstill be detected. Detecting the stimulus is not limited to thefrequency output, but can include, but is not limited to, a change infrequency, a change in q factor, a change in bandwidth, and acombination of these. These changes can result in increasing ordecreasing the power transferred between the reader and radio frequencyidentification tag. Increasing or decreasing the power transferredbetween the reader and radio frequency identification tag can result ina change of the readout of the tag.

In one approach, a specific electric connection within an RFID tag canbe disrupted, for example by cutting, and this connection can bereestablished by deposition of a chemiresistive sensing material byeither drawing or dropcasting. An RFID tag can include an integratedcircuit (IC) containing magnetic memory material where the tagidentification is stored. Depending on the sensing material and thestimulus, the tag can become readable and is classified as a “turn ONsensor,” or become unreadable and is classified as a “turn OFF sensor”.

In one method, the tag is not readable by a reader when no stimulus ispresent, because the resistance of the sensor is too high. When the tagis placed in the presence of a stimulus that causes the sensor to changeits resistance, the tag can become readable once the resistance valuecrosses a threshold value. This is a turn-on sensing method.

In another method, the tag can be readable by a reader when no analyteis present, because the resistance of the sensor is high enough to allowcurrent to flow through the integrated circuit. When the tag is placedin the presence of a stimulus that causes the sensor to change itsresistance, the tag can become unreadable once the resistance valuedrops below a certain threshold value. This is a turn-off sensingmethod.

In another method, instead of a turn-on sensing or a turn-off sensing, aseries of data can be collected, which can provide a quantitativeanalysis of a stimulus.

In another method, parallel integration can be used to integrate asensing material into a portion of the tag containing the integratedcircuit by drawing or dropcasting. This approach can “turn ON” or “turnOFF” detection of a stimulus, and can be complimentary to the firstapproach because requirements for resistance of the deposited sensingmaterial can be different (which may have an effect on the dynamic rangeand the detection limit of chemical sensors towards different analytes).

A radio frequency identification tag does not have to require a powersource. RFID tags can be either passive, active or battery-assistedpassive. An active tag has an on-board battery and periodicallytransmits its signal. A battery-assisted passive has a small battery onboard and is activated when in the presence of a RFID reader. A passivetag has no battery.

When detecting a stimulus comprising detecting an output from a radiofrequency identification tag including a sensor portion, the stimulusdoes not have to contact or interact with the entire surface of the tag.The sensor portion has a surface area less than the surface area of theradio frequency identification tag. The sensor portion can be located ona portion of a surface of the radio frequency identification tag, andthe stimulus can contact a portion of the surface of the radio frequencyidentification tag. In addition, the sensor portion can have multiplesensing locations, and a single tag can be used to detect more than onestimulus.

A system for detecting a stimulus comprising a radio frequencyidentification tag can include a sensor portion, the sensor portionconfigured to change resistivity when the radio frequency identificationtag contacts or interacts with the stimulus, whereby the resistivitychange alters an output of the radio frequency identification tag, and adetector detecting the output from the radio frequency identificationtag. The detector can include a reader. The reader can include a handheld frequency reader. A method of detecting a stimulus can includedetecting an output from a radio frequency identification tag includinga sensor portion.

The system can include a real time sensor. The system can include adosimeter, such as a radiation dosimeter, a chemical warfare agentdosimeter, or an analyte dosimeter, such as, for example, an ethylenedosimeter, a sulfur dosimeter, or an ozone dosimeter. The system can beused to monitor pollutants or chemicals relevant to occupational safety.Pollutants or chemicals can include fumes from automotive/equipmentexhaust, volatiles from manufacturing, painting, or cleaning, or vaporsin underground mines.

A sensor can include an electronic circuit comprising electroniccomponents. Electronic components can include resistors, transistors,capacitors, inductors and diodes, connected by conductive wires ortraces through which electric current can flow. The electricalconnection within the radio frequency identification tag can be altered.The resistivity of the sensor can change when the sensor is exposed to astimulus. Contacting or interacting with a stimulus can close thecircuit or open the circuit, or otherwise alter the properties of thecircuit.

A sensor can include a sensing material such as a metal, an organicmaterial, a dielectric material, a semiconductor material, a polymericmaterial, a biological material, a nanowire, a semiconductingnanoparticle, a carbon nanotube, a nanofiber, a carbon fiber, a carbonparticle, carbon paste, or conducting ink, or combination thereof. Asensing material can include organic electronics materials, dopedconjugated polymers, or inorganic materials. A sensing material caninclude biological molecule receptors, living cells, antibodies,aptamers, nucleic acids, functionalized biological molecules, or otherbiologically relevant moieties.

A tag for detecting a stimulus comprising a radio frequencyidentification tag can include a sensor portion, the sensor portionconfigured to change resistivity when the radio frequency identificationtag contacts or interacts with the stimulus, whereby the resistivitychange alters an output of the radio frequency identification tag,wherein the sensor portion includes a circuit, and wherein the sensorportion is configured to close the circuit or open the circuit whencontacted or having interacted with the stimulus. The tag can be worn asa badge for occupational health and safety personnel, militarypersonnel, etc., detecting a hazardous analyte or radiation.

A tag can include a substrate material. The substrate can include paper,plastic, a polymer, a metal, a metal oxide, a dielectric material, wood,leaves, skin, tissue, and so on. The substrate can include a metal oxidematerial. The substrate can be flexible; the substrate can be flat. Thetag can also be embedded inside other objects (e.g., inside a capsule ora wall) or inside living systems (e.g., implanted inside a body).

A tag can include an antenna, providing a link between a frequencyreader and a tag, receiving and transmitting a signal, and serving as aconduit that moves data back and forth. The antenna can include coilssurrounding a sensor; the antenna can include a dipole antenna. A tagcan include an antenna group including a plurality of antennas or anantenna array.

The ability to easily detect the existence of an analyte on a basesignal using an ON/OFF binary detection method is of increasing interestin today's society. A system using a portable reader, such as asmartphone, enables everyone to determine the status of certain analytesanywhere without complicated analysis of a signal. When the amount of ananalyte changes, a handheld frequency reader can turn on or turn off asignal, sending a notification of the presence or absence of theanalyte. Another advantage of using a smartphone is that it carrieswithin it many additional capabilities that can be coupled with chemicalsensing to increase utility. For instance, a smartphone reader canidentify a chemical spill and immediately send an emergency text oremail alert identifying position of a spill using GPS. Another examplecould be wireless networks that monitor spatiotemporal changes inconcentrations of chemical emissions and send emergency alerts when safethresholds are exceeded. Coupling of such capabilities can enableunprecedented utility of chemical sensors in everyday life.

A tag can serve as a binary logic element providing either a “1” or a“0” as pre-defined by functional sensor material, which offersadvantages in terms of simplicity of implementation and does not requireany sophistication by the end user. If viewed as a binary logic element,the tag could be used in further elaborations of that logic. Forinstance, a unique combination of the readout of multiple tags could beassigned to a specific meaning. For example, if three separate tags are“coded” for three separate analytes by virtue of the sensor materialsused to make them, then 2{circumflex over ( )}3 possible combinationsexist, which could each mean something unique and significant. Forexample, if those analytes were food related, then one could possiblydetermine which type of food the sensors are attached to based on acombination of tag read-out, within a certain probability. Anotherexample would be three tags that are “coded” with the same sensormaterial that has been designed to react at different concentrations ofanalyte. The combination of tag readout would allow one to determine,within some margin of error, the concentration of the analyte ofinterest.

The binary on/off readability of CARDs by the smartphone can be apowerful approach for converting analog physical inputs (presence orabsence of a chemical vapor within a defined threshold) into a digitizedoutput (1 and 0, respectively) that conveys meaningful information aboutthe local chemical environment of the CARDs. The advantage of abinary-readout is that it is the simplest possible output representationof input information, and hence allows modular multiplexing of differentCARD combinations. This analytical approach has practical limitations inits implementation; however, it may be particularly useful inresource-constrained scenarios or high throughput applications whereinformation about the presence or absence of specific chemicals atspecified thresholds is critically important. Such applications mayinclude detection of an acceptable threshold (e.g., permissible exposurelimit for a chemical) that provides valuable actionable information indynamic, complex environments (e.g., chemical release within a publicspace). Even under circumstances wherein the chemical of interest can bereadily detected by the human nose, a differentiating feature of asmartphone-based sensing strategy over human-olfactory detection orvisual inspection of a colorimetric test is the ability to efficientlybring sensed information into the information technology infrastructure.

An inexpensive, simple, rapid, and modular approach for convertingcommercially available NFC tags into chemically actuated devices cancommunicate with a smartphone via radio waves. This approach enableselectronic wireless, non-line-of-sight detection and discrimination ofgases and vapors at part-per-million and part-per-thousandconcentrations. This technology provides binary (“on”/“off”) informationabout the presence or absence of a chemical analyte regarding designatedconcentration thresholds, (e.g., NIOSH STEL) within the localenvironment of the sensor tag, and is capable of differentiatingmultiple concentrations of one analyte or multiple analytes usingmulti-tag logic. The general sensing strategy involving wirelesscommunication between NFC tags and smartphones is modular and can begeneralized to incorporate many types of chemiresponsive materials toenable selective detection of diverse chemical changes. Nevertheless,the significant challenges that remain to realize the full potential ofthis wireless sensing approach includes: (i) chemical and materialsscience innovations to improve the sensitivity and selectivity ofchemiresponsive materials to chemical analytes; (ii) improvingdevice-to-device performance reproducibility by advancing thestate-of-the-art of nanostructured carbon deposition techniques and;(iii) enabling continuum measurement CARD readout capabilities. Thecombination of chemical sensing with other capabilities within thesmartphone (e.g., GPS) may enable additional utility in applicationsinvolving tracking and tracing. As a result of the portability andincreasingly ubiquitous use of smartphones and mobile devices, thisplatform can enable applications in personalized and widely distributedchemical sensing wherein the acquisition of chemical or physicalinformation was previously unattainable.

A chemically-degradable polymer is a polymer whose disassembly can betriggered by an interaction with a stimulant or analyte. In certainembodiments, the stimulant can be an analyte.

A supramolecular polymer is a polymer whose monomeric units holdtogether via highly directional and reversible non-covalentinteractions. In certain embodiments, the non-covalent interactions canbe hydrogen bonding, π-π interactions, or metal coordination-basedinteractions. In certain embodiments, the supramolecular polymer can beone-dimensional, two-dimensional or three-dimensional.

A metallo-supramolecular polymer is a polymer whose monomeric units holdtogether by metal coordination-based interactions.

Disclosed herein is a tag for detecting an analyte including a radiofrequency identification tag including a sensor portion, the sensorportion configured to change resistivity when the radio frequencyidentification tag contacts or interacts with an analyte, whereby theresistivity change alters an output of the radio frequencyidentification tag, wherein the sensor portion includes a circuit, andwherein the sensor portion is configured to activate the circuit ordeactivate the circuit when contacted or having interacted with theanalyte, where the sensor portion includes a conductive materialassociated with a chemically-degradable polymer. In certain embodiments,the conductive material can include carbon nanotubes, graphene, metaloxides, or metal-organic-framework.

In certain embodiments, the chemically degradable polymer can include aligand and a metal ion. The ligand can be a multi-dentate ligand capableof binding to two or more metal ions. In certain embodiments, thechemically degradable polymer can include a metallo-supramolecularpolymer. In certain embodiments, single walled carbon nanotubes (SWCNTs)can be wrapped with metallo-supramolecular polymers for sensory deviceswith a dosimetric (time- and concentration-integrated) increase inelectrical conductivity that is triggered by electrophilic chemicalsubstances such as diethylchlorophosphate, a nerve agent simulant. Themechanism of this process involves the disassembly of the supramolecularpolymer. It can be used in a wireless inductively powered sensing systembased on near field communication technology (NFC). Specifically, thedosimeters can be powered and read wirelessly with conventionalsmartphones to create sensors with ultra-trace detection limits.

In certain embodiments, a chemical dosimeter can include SWCNTs wrappedwith a metallo-supramolecular polymer (MSP) that displays large, time-and concentration-integrated chemiresistive responses via MSPdisassembly triggered by analyte molecules. In this system,supramolecular polymers (see Aida, T.; Meijer, E. W.; Stupp, S. I.Science 2012, 335, 813-817, Wojtecki, R. J.; Meador, M. A.; Rowan, S. J.Nat. Mater. 2011, 10, 14-27, Whittell, G. R.; Hager, M. D.; Schubert, U.S.; Manners, I. Nat. Mater. 2011, 10, 176-188., and Yang, L.; Tan, X.;Wang, Z.; Zhang, X. Chem. Rev. 2015, 115, 7196-7239, each of which isincorporated by reference in its entirety) can wrap and isolate CNTs anddisassemble in response to chemical stimuli.

Wrapping of SWCNTs with chemically-degradable polymers is a powerfulstrategy for the development of advanced chemiresistive dosimetricsensors. The choice of the supramolecular polymer is crucial to thesedesigns and the polymer must generate stable dispersions that can beused to create solid composites that prevent low resistivity inter-SWCNTcontacts. After disassembly, the molecules must release the SWCNTs andnot quench their conductivity to generate low resistivity networks withlow resistivity inter-SWCNT junctions. Additional families of highlysensitive chemiresistive dosimeters can be created based on thisconcept.

SWCNT wrapped with MSPs can display large time- andconcentration-integrated chemiresistive responses as a result of atriggered disassembly of the MSPs induced by strong electrophiles suchas DECP and SOCl₂. Various approaches including ligand design, selectionof metal ions, and optimizing SWCNT dispersion conditions aredemonstrated to be effective to increase sensitivity to harmfulanalytes. Demetallation (disassembly) of the MSP degrades the SWCNTwrapper, thereby decreasing inter-SWCNT resistance at junctions,resulting in large (>1,000%) increases in conductivity. The highlysensitive and irreversible chemiresistive chemical responses enablewireless chemical sensing with NFC technology.

This system is specifically targeted for strong electrophilic analytessuch as diethylchlorophosphate (DECP, a reactive simulant of nerveagents) and thionyl chloride (SOCl₂, a reactive simulant of pulmonaryagents). Critical to the design of this chemical dosimeters is thecreation of a system wherein the cooperative interactions of MSP arecapable of effectively dispersing SWCNTs and maintaining them in aninsulated, highly resistive state, while the MSP monomers alone interactsufficiently weakly with SWCNTs such that they are ineffective atcreating a dispersion. With these conditions established, triggereddisassembly of the MSP can generate a conductive network with strongSWCNT-SWCNT interactions. The large and irreversible chemiresistiveresponse associated with this process can be easily detected and thisfeature can illustrated using a commercial smartphone and modifiednear-field communication (NFC) tags to create a wireless system todetect harmful electrophiles.

Formation of MSP. Polarizable polycyclic aromatic molecules exhibitstrong van der Waals interactions with SWCNTs, and as a resultanthracene-based ligands (AL) was chosen shown in FIG. 1A to producedispersions. The anthracene core is substituted with two n-propylsalicylaldimine motifs, which are expected to form a square planarcomplex with Cu²⁺ or Ni²⁺ ions. See Sacooni, L.; Ciampolini, M. J. Chem.Soc. 1964, 276-280, and Chakravorty, A.; Fennessey, J. P.; Holm, R. H.Inorg. Chem. 1965, 4, 26-33, each of which is incorporated by referencein its entirety. Two n-octyl chains were added to the 9,10-positions ofthe anthracene to solubilize the SWCNT dispersion. The ability of thisligand to be converted into a ladder polymer with transition metallinkages was studied by titration with Cu²⁺ or Ni²⁺ ions. The UV-Visabsorption of AL varied upon addition of Cu²⁺ and abruptly saturatedwith one equivalent of Cu²⁺ (FIGS. 1B and 1C). FIGS. 1B and 1C showUV-Vis titration experiments of AL (7.0×10⁻⁵ M, o-DCB/methanol=9/1) withCu(AcO)₂.H₂O (10.6×mM, methanol) at room temperature. The optical pathlength was 10 mm. This result indicates that salicylaldimine unitsstrongly coordinate Cu²⁺, yielding MSP(Cu). In contrast, the Ni²⁺titration curve with AL lacked a clear saturation point (FIG. 20),suggesting that MSP(Ni) is oligomeric in solution. In FIG. 20, UV-Vistitration experiments of AL (7.0×10⁻⁵ M, toluene/methanol=2/1) withNi(AcO)₂.4H₂O (10.6 mM, methanol) at room temperature. Optical lengthwas 10 mm. Gel permeation chromatography experiment reveals that MSP(Cu)displays a radius of gyration that is comparable to that ofit-conjugated polymer with M_(n)=9.0 k, thereby confirming that MSP(Cu)is approximately 15-mers on average (FIGS. 21A-21C). FIG. 21A showschemical structures of compounds used for gel permeation chromatography(GPC) study using Bio-Beads S-X1 (eluent: o-DCB). FIG. 21B shows GPCexperiments for the mixtures of AL and PFO, and clearly indicates thatelution time of AL is slower than that of PFO. PFO was prepared byNi(0)-catalyzed cross-coupling polymerization of9,9-Di-(2′-ethylhexyl)-2,7-dibromofluorene. See Yang, Y.; Pei, Q.;Heeger, A. J. J. Appl. Phys. 1996, 74, 934-939, which is incorporated byreference in its entirety. FIG. 21C shows GPC experiments for themixtures of MSP(Cu), PFO, and OxP. See Hill, J. P.; Ariga, K.;Schumacher, A. L.; Karr, P. A.; D'Souza, F. J. Porphyr. Phthalocyanines2007, 11, 390-396, which is incorporated by reference in its entirety.Elution time of MSP(Cu) is faster than that of OxP, and comparable tothat of PFO. Note that MSP(Cu) made from 0.5:0.5:1.0 mixture of ALOx,AL, and Cu²⁺ (by mole) demonstrated similar results in the GPCexperiments. The polymeric structure of MSP(Cu) was also confirmed byassembling it on a graphite surface and imaging by scanning tunnelingmicroscope (STM). As shown in FIG. 1D, these studies revealed linear androd-like assemblies of MSP (Cu) with domain size of 10-50 nm,corresponding to 10-50 mers.

Wrapping SWCNT with MSP. A key element of the design is that themonomers are not sufficient to disperse SWCNTs, but that the collectiveproperties of the supramolecular polymer create a highly stabledispersion. See Toshimitsu, F.; Nakashima, N. Nat. Commun. 2014, 5,5041, and Llanes-Pallas, A.; Yoosaf, K.; Traboulsi, H.; Mohanraj, J.;Seldrum, T.; Dumont, J.; Minoia, A.; Lazzaroni, R.; Armaroli, N.;Bonifazi, D. J. Am. Chem. Soc. 2011, 133, 15412-15424, each of which isincorporated by reference in entirety. AL meets these criteria and isnot capable of forming stable SWCNT dispersions in o-dichlorobenzene(o-DCB), however with sonication (5 min) in the presence of Cu²⁺ or Ni²⁺ions homogeneous stable SWCNT dispersions are created (FIG. 2A). In FIG.2A, equal equivalents of Cu(AcO)₂.H₂O or Ni(AcO)₂.4H₂O in methanol (10.6mM, 82 μL) and AL (0.5 mg) in o-DCB (1 mL) are combined with SWCNTs (0.1mg), and then sonicated for 5 min. In contrast, similar procedurescomplexing AL with Zn²⁺ and Co²⁺ did not produce stable SWCNTdispersions, presumably due to the lack of square-planar configurationabout the metal ion (FIGS. 22A-22B). FIG. 22A shows dispersion of SWCNTby metal ligand complexes of AL. AL itself is not capable of dispersingSWCNT. Addition of Ni²⁺ and Cu²⁺ (as acetate salts, 1 equivalent to AL)lead to homogeneous dispersion of SWCNT, while addition of Zn²⁺ and Co²⁺did not work for dispersion of SWCNT. FIG. 22B shows chemiresistiveresponse of SWCNT+MSP sensors upon exposure to saturated acetylchloride. Mixing ratio of AL and SWCNT was fixed to 5:1. Amount of metalion is 1 molar equivalent to AL. Fixed parameters: SWCNT (0.02 mg),o-DCB (0.2 mL). Only MSP(Cu) and MSP(Ni) demonstrated large response toacetyl chloride. This result strongly suggests that homogeneousdispersion (wrapping) of SWCNT is a key for sensing response.

To determine if small molecule square planar metal complexes aresufficient, Ni²⁺ complex of n-dodecylsalicylaldimine (DSA(Ni)) wasinvestigated, which has an established square planar structure (seeChakravorty, A.; Fennessey, J. P.; Holm, R. H. Inorg. Chem.1965, 4,26-33, which is incorporated by reference in its entirety) and find thatthis monomeric system is incapable of producing stable SWCNT dispersions(FIGS. 23A-23B). FIG. 23A shows mixture of SWCNT by DSA(Ni) in o-DCBafter sonication for 30 min. DSA(Ni) is not capable of dispersing SWCNT.FIG. 23B shows chemiresistive response of SWCNT mixed with DSA(Ni) uponexposure to saturated DMCP. Mixing ratio of DSA(Ni) and SWCNT was 5:1.Fixed parameters: SWCNT (0.02 mg), o-DCB (0.2 mL).

As a result, it would appear that the MSP structure having square planarmetal center, polarizable π electron system, and polymeric structure arecollectively responsible for producing well behaved SWCNT dispersions.The quality of the dispersions is further confirmed by UV-Vis-NIRspectra of solutions of SWCNT/MSP(Cu) and SWCNT/MSP(Ni) that revealedwell-resolved absorptions from E₁₁ transitions of SWCNT, which isindicative of isolated (debundled) SWCNTs (optical pathlength: 1 mm)(FIG. 2B). See Samanta, S. K.; Fritsch, M.; Scherf, U.; Gomulya, W.;Bisri, S. Z.; Loi, M. A. Acc. Chem. Res. 2014, 47, 2446-2456, which isincorporated by reference in its entirety. Scanning electron microscopy(SEM) images of SWCNT/MSP(Cu) drop-cast film revealed SWCNTs having morelinear and narrow structures relative to pristine SWCNTs, alsosupporting the formation of isolated wrapped SWCNTs (FIGS. 2C and 24).In FIG. 2C, the concentration of SWCNT (0.1 mg/mL) was identical to thatused to create networks for the sensing studies. In FIG. 24, pristineSWCNT sonicated in o-DCB was drop-cast on Si substrate. The assembly ofisolated SWCNTs into random porous network structures facilitates thediffusion of analyte molecules into the film and the triggeredgeneration of enhanced electronic conduction pathways via disassembly ofthe polymer wrappers.

Sensing properties of SWCNT/MSP. Chemiresistive sensors were prepared bydrop-casting 0.5 μL of SWCNT/MSP(Cu) or SWCNT/MSP(Ni) dispersions oninterdigitated gold electrodes (0.2 mm gaps), and the variation inconductivity upon exposure to various types of analyte vapors, includingDECP, is measured by detecting the current with an applied potential of0.1 V (FIG. 3A). Only very small amounts of material are required tomake a sensor and up to 4,000 sensors can be prepared from 1 mg of AL.The quality of the SWCNT dispersion enables high sensor fabricationreproducibility from batch-to-batch (Table 1). See Zhang, Y.; Xu, M.;Bunes, B. R.; Wu, N.; Gross, D. E.; Moore, J. S.; Zang, L. ACS Appl.Mater. Interfaces 2015, 7, 7471-7475, which is incorporated by referencein its entirety.

TABLE 1 Resistance of 9 sensors prepared by drop-casting 0.5 μL ofSWCNT/MSP(Cu) dispersion in o-DCB on interdigitated gold electrodes (0.2mm gap). Sample No. Resistance (kΩ) 1 19.26 2 18.22 3 20.58 4 13.61 524.67 6 22.38 7 35.01 8 37.23 9 30.42 Average 24.60 Standard Deviation8.01

The SWCNT/MSP composites proved effective in generating high sensitivityto target analytes as shown in FIG. 3B. Specifically, SWCNT/MSP(Cu) andSWCNT/MSP(Ni) display large increases in conductivity upon exposure to10 ppm DECP (in N2) when compared to the responses of sensors createdwith pristine-SWCNTs and SWCNTs wrapped bypoly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO), which were prepared underthe same conditions. Two samples of SWCNT/MSP were tested for confirmingreproducibility (shown by solid and dotted line). Initial resistance ofsensors were 15 kΩ-30 kΩ. PFO stabilized SWCNT dispersions have beenstudied previously were chosen as a non-responsive control material.See, Nish, A.; Hwang, J.-Y.; Doig, J.; Nicholas, R. J. Nat. Nanotech.2007, 2, 640-646, which is incorporated by reference in its entirety. Itis also noteworthy that SWCNT/MSP exhibits enhanced sensitivity tospecific chemicals such as DECP, while responses to water as well as anumber of common volatile organic compounds (VOCs) are much lower andsimilar what is observed for the pristine-SWCNT and SWCNT/PFO controls(FIG. 3C). FIG. 3C shows chemiresisitve responses of SWCNT-basedchemiresistive sensors upon 50 s exposure to various vapors in N₂(concentration in ppm given in parentheses). Chemiresisitve responses tothese analytes were nearly saturated within 50 s. Moreover, in mostcases, the response to non-target analytes is an increase inresistivity, consistent with swelling- or hole-quenching typetransduction mechanism. See Fennell, J. F., Jr.; Liu, S. F.; Azzarelli,J. M.; Weis, J. G.; Rochat, S.; Mirica, K. A.; Ravnsbæk, J. B.; Swager,T. M. Angew. Chem. Int. Ed. 2016, 55, 1266-1281, which is incorporatedby reference in its entirety. This is opposite that observed for DECPwherein the disassembly of the MSP wrapper generates lower resistancejunctions between the SWCNTs.

Optimization of SWCNT/MSP(Cu) sensor for enhanced response. TheSWCNT/MSP(Cu) composition was optimized by monitoring the chemiresistiveresponse to concentrated dimethylchlorophosphate (DMCP) vapor in dryargon (Ar). The 1:5 (by weight) mixture of SWCNT to MSP(Cu) displayed ahigher response than 1:1, 1:2, and 1:10 mixtures (FIG. 25). Mixing ratioof AL and SWCNT (in weight) was varied as 1:1, 2:1. 5:1, and 10:1. 5:1demonstrated the largest response. Fixed parameters: SWCNT (0.02 mg),o-DCB (0.2 mL), 1 equivalent Cu²⁺ for AL. It is also found that the useof 0.5 eq. of Cu²⁺ lead to lower response (FIG. 26), suggesting thatcomplete polymerization of MSP is important to achieve the maximumresponse. Mixing ratio of AL and Cu²⁺ was varied as 1:0.5, 1:1, 1:1.5,and 1:2, and 1:0.5 demonstrated reduced response. Fixed parameters:SWCNT (0.02 mg), AL (0.1 mg), o-DCB (0.2 mL). The change of solvent fromo-DCB to a mixture of o-DCB and toluene (1:4 by volume) led to a twofoldincrease of the response to DMCP, and a further twofold increase wasachieved when the supernatant of centrifuged solution was used (FIGS.27A-27B). FIG. 27A shows chemiresistive response of SWCNT+MSP(Cu)sensors upon exposure to saturated DMCP. Mixed solvents of o-DCB andtoluene (1:0, 1:1, 1:2, 1:4, and 0:1 in volume) were used for dispersionof SWCNT+MSP(Cu). The dispersion was used for sensing withoutcentrifuging. Fixed parameters: SWCNT (0.02 mg), AL (0.1 mg), Cu²⁺(1molar equivalent to AL), total volume of mixed solvent (0.2 mL). FIG.27B shows chemiresistive response of SWCNT+MSP(Cu) sensors afterapplying centrifuge. Supernatant solution demonstrated the largestresponse to DMCP. Fixed parameters: SWCNT (0.02 mg), AL (0.1 mg), Cu²⁺(1 equivalent to AL), o-DCB:Toluene=1:4 (0.2 mL).

The drop-cast film of the SWCNT/MSP(Cu) supernatant o-DCB/toluenesolution gave sensors with higher initial resistance (ca. 2 MΩ for 5μL×3 drops) than those made from the as formed dispersion (ca. 100 kΩfor 5 μL×3 drops), suggesting that a minority amount of bundled SWCNTsthat are removed by centerfugation are sufficient to cause lowresistance pathways that decrease the sensitivity. In addition, whencompared with SWCNT/MSP(Cu) dispersed by o-DCB, the UV-Vis-NIR spectrumof the supernatant solution revealed reduced signal from MSP(Cu)chromophore appearing at 750 nm and 940 nm (FIGS. 28A-28B). In FIG. 28B,background signals from o-DCB are denoted by asterisk. These resultssuggest that toluene (a poor solvent for MSP(Cu)) serves to removeexcess MSP(Cu). Surplus polymer that impedes optimal SWCNT-SWCNTcontacts with the analyte triggered unwrapping of MSP(Cu) is also likelyto be detrimental to the sensor sensitivity. The addition of toluenedoesn't affect the E₁₁ transitions of SWCNT, indicating that the SWCNTcomposition (i.e., chirality or diameter) is not effected by the changein solvent. See Hwang, J.-Y.; Nish, A.; Doig, J.; Douven, S.; Chen,C.-W.; Chen, L.-C.; Nicholas, R. J. J. Am. Chem. Soc. 2008, 130,3543-3553, which is incorporated by reference in its entirety. FIG. 4Ashows conductance traces of optimized SWCNT/MSP(Cu) chemiresistivesensors upon exposure to 0.1, 1.0, and 10 ppm DECP in N₂. A mixture ofo-DCB and toluene (1:4 by volume) was used for dispersing SWCNT/MSP(Cu),and the supernatant of the centrifuged solution was drop-cast on theelectrode to prepare sensors. The initial resistance range of thesensors was 700 kΩ-2,000 kΩ. Arrows indicate when injection of gasstarted. Asterisk denotes DECP. Black dotted lines indicate the slope ofthe traces estimated by linear approximation. Baseline correction wasapplied to the 0.1 ppm sensing trace (see FIGS. 34A-34B). FIG. 34A showsconductance traces of optimized SWCNT/MSP(Cu) chemiresistive sensorsmade from 1:1 mixtures of AL and Cu²⁺ (in mole) upon exposure to 0.1 ppmDECP in N₂. A mixture of o-DCB and toluene (1:4 by volume) was used fordispersing SWCNT/MSP(Cu), and the supernatant of the centrifugedsolution was used for preparing sensors. Blue solid line, green dotlines, red solid line indicate original data, baseline,baseline-corrected data, respectively. Baseline corrected data was usedfor FIG. 34A. FIG. 34B shows conductance traces of optimizedSWCNT/MSP(Cu) chemiresistive sensors made from 0.5:0.5:1.0 mixtures ofALOx, AL, and Cu²⁺ (in mole) upon exposure to 0.1 ppm DECP in N₂. Amixture of o-DCB and toluene (1:4 by volume) was used for dispersingSWCNT/MSP(Cu), and the supernatant of the centrifuged solution was usedfor preparing sensors. Blue solid line, green dot lines, red solid lineindicate original data, baseline, baseline-corrected data, respectively.Baseline corrected data was used for FIG. 4B. As shown in FIG. 4A, theoptimized SWCNT/MSP(Cu) sensor demonstrated a 2,000% increase inconductivity upon exposure to 10 ppm DECP. Accordingly, optimizationimproved the response by 6×, and is 40 and 200 times larger than that ofpristine SWCNT and SWCNT/PFO controls, respectively (in comparison withFIG. 3B). The saturated chemiresistive responses for 1.0 ppm and 0.1 ppmDECP were ca. 600-700%, and the slope (rate) of increasing conductivitydecreased as the concentration of DECP decrease.

Investigating the sensing mechanism. As expected, SWCNT/MSP(Cu) as wellas SWCNT/MSP(Ni) displays increases in conductivity upon exposure toother strong electrophiles such as acetyl chloride, trifluoroaceticacid, and SOCl₂ (FIGS. 22 and 29). FIG. 29A shows chemiresisitiveresponse of SWCNT+MSP (prepared in o-DCB) for trifluoroacetic acid. Notethat pristine SWCNT and PFO-wrapped SWCNT also demonstrate strongresponse. FIG. 29B shows chemiresisitive response of SWCNT+MSP(Cu)(prepared in o-DCB:Toluene=1:4, non centrifuged) for thionyl chloride.

To investigate the sensing mechanism, diamagnetic square planar Ni²⁺complex of n-dodecylsalicylaldimine (DSA(Ni)) was used as a modelcompound (FIGS. 30A-30B). See Chakravorty, A.; Fennessey, J. P.; Holm,R. H. Inorg. Chem. 1965, 4, 26-33, which is incorporated by reference inits entirety. After bubbling with DMCP for 3 min the ¹H-NMR spectrumindicates that the DSA(Ni) is completely demetallated and onlydissociated free DSA is detected. The formation of an iminium ion (seeWeinreb, S. M.; Scola, P. M. Chem. Rev. 1989, 89, 1525-1534, which isincorporated by reference in its entirety) is a likely intermediate stepof demetallation; however such a highly reactive intermediate will notpersist to allow detection. When acetyl chloride was added to DSA(Ni),free DSA as well as the DSA acetyl-ester were observed in ¹H-NMRspectrum (FIGS. 30A-30B). This result indicates that there may bemultiple reaction pathways for demetallation of MSP and/or postdemetallation chemical transformations. UV-Vis-NIR and MALDI-TOF MSexperiments also support that demetallation of MSP(Cu) occurs withexposure to DMCP (FIGS. 31A-31C). FIG. 31A shows MALDI-TOF-MS spectra ofSWCNT+MSP(Cu) before and after exposure to DMCP. Mass signals fromcomplexes of AL and Cu were disappeared after exposure to DMCP. FIG. 31Bshows UV-Vis-NIR spectra of SWCNT+MSP(Cu) film on quartz before andafter exposure to DMCP. FIG. 31C shows IR spectra of DSA(Ni) in CCl₄before and after bubbling with DMCP vapor. For comparison, IR spectrumof DSA is also shown. Note that DMCP was added with P4VP for trappingHCl, and DMCP vapor was delivered with dry argon.

Fragments of MSP (including AL itself) are not effective at wrapping ordispersing SWCNTs; bubbling DMCP vapor through a SWCNT/MSP(Cu)dispersion in o-DCB gives immediate precipitation (FIG. 32). FIG. 32shows precipitation of SWCNT+MSP(Cu) dispersion in o-DCB immediatelyafter bubbling the dispersion with DMCP. In contrast, SWCNT dispersed byPFO was not precipitated at all even after bubbling with DMCP vapor forseveral minutes. In contrast, SWCNTs dispersed using PFO do notprecipitate even after several minutes of bubbling DMCP vapor into thesolution. PFO does not react with DMCP and it is clear that the chemicaldisassembly of the MSP is a key component of this system's response tostrong electrophiles.

Modification of AL with oxime for improved response to DECP. In order tofurther increase the transitional response (i.e., slope of increasingconductivity) to DECP, n-propyl imines in AL were substituted by oximesto form ALOx (FIG. 4B). Fast and irreversible reactivity of oximes withphosphorous electrophiles, which is explained as by the α-effect, hasbeen investigated extensively, and underlies the structure-functionbasis for nerve agent antidotes (e.g., pralidoxime shown in FIG. 4B).See Dale, T. J.; Rebek, J., Jr. Agnew. Chem. Int. Ed. 2009, 48,7850-7852, which is incorporated by reference in its entirety. AlthoughALOx forms a strong metal ligand complex with Cu²⁺ in 1:1 molarstoichiometry (FIGS. 33A-33B), MSP(Cu) made from ALOx was not capable ofdispersing SWCNTs. FIGS. 33A-33B show UV-Vis titration experiments ofALOx (7.0×10⁻⁵M, o-DCB/methanol=9/1) with Cu(AcO)₂.H₂O (10.6 mM,methanol) at room temperature. The optical path length was 10 mm. Notethat aggregation was observed upon addition of Cu²⁺. Thus, compositeMSP(Cu) made from 0.5:0.5:1.0 mixture of ALOx, AL, and Cu²⁺ (by mole)was utilized to disperse SWCNTs in a solution of o-DCB and toluene (1:4by volume). FIG. 4C shows conductance traces of optimized SWCNT/MSP(Cu)chemiresistive sensors made from 0.5:0.5:1.0 (by mole) mixtures of ALOx,AL, and Cu²⁺ upon exposure to 0.1, 1.0, and 10 ppm DECP in N₂. A mixtureof o-DCB and toluene (1:4 by volume) was used for dispersingSWCNT/MSP(Cu), and the supernatant of the centrifuged solution wasdrop-cast on the electrode for preparing sensors. The initial resistancerange of sensors was 700-2,000 kΩ. Chemiresistive sensors were preparedfrom the supernatant of the centrifuged mixture, and FIG. 4C shows thatthe slope of increasing conductivity as well as saturated response aresignificantly improved by incorporating ALOx into the sensorformulation. The slope of chemiresistive response to DECP decreases withdecreasing DECP concentration, while the response saturates at a similarlevel. This result indicates a nearly ideal dosimetric sensing responsethat is directly correlated with the number of analyte (DECP) moleculesthat MSP encounters.

This dosimetric behavior is consistent with a mechanism wherein theSWCNT/MSP network is initially in a highly resistive form, wherein theMSP groups are preventing optimal charge transport across SWCNT-SWCNTjunctions. DECP triggered disassembly of the MSP wrapper enhances theconductivity and at lower levels of disassembly new independent pathwaysare being established with each improved SWCNT-SWCNT junction. As theMSP is progressively disassembled, new bifurcated and redundant pathwayshave less of an overall effect and the relative response decreases. Thissensing mechanism is dosimetric giving a time- andconcentration-integrated response. As indicated previously, dosimetersare particularly useful in monitoring acutely toxic chemical substancesat extremely low concentrations.^(6, 26) Although the presentinvestigations are limited to chemiresistors, additional sensitivityenhancements may be possible if the sensing materials were to beintegrated into devices that function in capacitive or field effecttransistor modes. See Kauffman, D. R.; Star, A. Angew. Chem. Int. Ed.2008, 47, 6550-6570, and Snow, E. S.; Perkins, F. K.; Robinson, J. A.Chem. Soc. Rev. 2006, 35, 790-798, each of which is incorporated byreference in its entirety. Wireless chemical sensing. The utility of thelarge and irreversible chemiresistive response of SWCNT/MSP(Cu) sensorswas demonstrated by wireless chemical sensing under ambient conditions.To this end, a near-field communication (NFC) tag (see Azzarelli, J. M.;Mirica, K. A.; Ravnsbæk, J. B.; Swager, T. M. Proc. Natl. Acad. Sci. USA2014, 111, 18162-18166, which is incorporated by reference in itsentirety) was modified such that a commercial smartphone can be used todetect trace toxic chemicals. Using a Samsung Galaxy S4 (SGS4), aturn-on dosimetric sensor can be prepared by inserting resistors inseries with the antenna (L) of NFC tag (FIG. 5). R_(IC), C, L, and Rdenote the integrated circuit, capacitor, antenna, and resistor,respectively. If the inserted resistance is higher than 2.2 kΩ, themodified NFC tag was unreadable by SGS4 because resistance is highenough to prohibit the NFC tag from creating a resonant circuit at 13.56MHz (FIG. 35A). In FIGS. 35B-35C, solid lines correspond with tags thatare readable by smartphone. Dotted lines correspond with tags that areunreadable by smartphone. In contrast, the modified NFC tag becomesreadable by SGS4 when the inserted resistance is lower than 1.0 kΩ.Thus, approximately 100% increase in conductivity (i.e., change from 2.2kΩ to 1.0 kΩ) is required to switch between the unreadable and readablestate, and hence the chemiresistive dosimetric sensor is well suited tocreating a turn-on NFC tag (FIGS. 4A and 4C). As a demonstration, an NFCtag modified by the SWCNT/MSP(Cu) material (initial resistance=3.6 kΩ)is initially unreadable by SGS4, but converts to a readable state(resistance=0.79 kΩ) after 5 s exposure to 10 ppm SOCl₂ in air. Themodified NFC tag becomes readable by a smart phone after 5 s exposure to10 ppm SOCl₂ at ambient condition (in air, 17.1° C., relativehumidity=16.2%). A mixture of o-DCB and toluene (1:1 by volume) was usedfor dispersing SWCNT/MSP(Cu), and the supernatant of the centrifugedsolution was used for preparing sensors. The NFC tag remains readable bySGS4 after more than 1 week of storage in ambient atmosphere, and hencethe cumulative SOCl₂ exposure history can be established even after anextended period of time.

This non-volatile memory is advantageous for wireless sensing especiallywhen continuous monitoring is economically unfeasible or difficult as aresult of limited sampling opportunities. This specific sensing systemcould find utility for leak detection from Li—SOCl₂ backup batteriescommonly used in medical instruments, fire alarms, and military systems.

An alternative turn-off dosimetric sensor can be prepared by changingthe circuit design. The combination of turn-on and turn-off sensor modescan enhance the reliability of a sensing system. These modificationtechniques to conventional NFC tags facilitate deployment of the methodsas chemical sensors for safety and security management.

EXAMPLES

Materials

All solvents were of ACS reagent grade or better, and used withoutpurification unless otherwise noted. Tetrahydrofuran, dimethylformamide,and dichloromethane for syntheses were dried over activated molecularsieves (4 Å). Deuterated solvents for NMR spectroscopy were purchasedfrom Cambridge Isotope Laboratories, Inc. All reagent grade materialswere purchased from Sigma-Aldrich, Toyo Chemical Industry, Alfa Aesar,or Macron Fine Chemicals, and used without further purification. Thinlayer chromatography (Merck silica gel 60 F254 plates) was used formonitoring reaction progress. Silica gel (60 Å pore size, 230-400 mesh)was purchased from Sigma-Aldrich. Bio-Beads S-X1 Support (styrenedivinylbenzene beads, 1% crosslink, 40-80 μm bead size, 600-14000 g/molexclusion range) from BIO-RAD was used for size exclusionchromatography. Poly(9,9-di-n-octylfluorenyl-2,7-diyl) with M_(w)>20 kwas obtained from Aldrich. Purified SWCNT (Lot: PT102210) was obtainedfrom Nano-C. 2,6-Dimethoxy-anthraquinone was synthesized according to aliterature procedure. See Cammidge, A. N.; Goddard, V. H. M. LiquidCrystals 2008, 35, 1145-1150, which is incorporated by reference in itsentirety.

2. Methods

General Methods

¹H and ¹³C NMR spectra were acquired by Bruker Avance Spectrometeroperating at 400 MHz and 101 MHz for ¹H and ¹³C, respectively. Chemicalshifts are referenced to residual NMR solvent peaks (CDCl₃: 7.24 ppm for¹H and 77.23 for ¹³C). MALDI-TOF MS was measured using Bruker OmniflexMALDI-TOF instrument. Dithranol was used as a matrix. High-resolutionmass spectra (HRMS) were obtained by Bruker Daltonics APEXIV 4.7 TeslaFT-ICR-MS employing electrospray (ESI) or direct analysis in real time(DART) as the ionization technique. Absorption spectra were measuredusing an Agilent Cary 4000 Series UV-Vis-NIR spectrophotometer. FT-IRspectra were acquired using a Thermo Scientific Nicolet 6700. Ge crystalwas used for ATR mode. For liquid state FT-IR spectra (transparentmode), Specac Omni Cell and NaCl crystals were used. Interdigitatedmicroelectrode (CC1.W1) with electrode gap of 200 μm was purchased fromBVT Technologies. Scanning electron microscope was measured using JEOL6010LA with accelerating voltage of 2.0-10.0 kV.

Dispersion of SWCNT and Device Fabrication

In a typical device, 0.02 mg of SWCNT and 0.1 mg of AL were suspended in0.2 mL of o-DCB, and then metal acetate dissolved in methanol (10.6 mM,16.4 μL) was added. The suspension was treated in an ultrasonic bath for10 min at room temperature. The suspension was centrifuged (6900×g,12000 rpm, 10 min, mini-centrifuge from Bio Lion) if necessary, andsupernatant solution (top 50%) was collected. The dispersion (ca. 0.5μl) was drop-cast on interdigitated microelectrode (CC1.W1 form BVTTechnologies). The solvent was removed in air. The drop-casting of thedispersion was repeated until the resistance of SWCNT network (measuredby a multimeter) reached desired values. Sensors were kept in dry N₂.

Gas Detection Measurements (Wired)

Gas detection measurements were acquired by using a test clip fittedwith a PTFE chamber to connect the interdigitated microelectrodes to aPalmSens EmStat potentiostat with a MUX16 multiplexer (FIG. 36). Formeasuring device response to volatile liquid organic compounds and towater, a KIN-TEK gas generator system was used to produce analyte gaswith known concentration. Flow rate of analyte was adjusted by gas flowmeter obtained from Matheson. The chemiresistive device was enclosed ina PTFE chamber. The potentiostat was used to apply a constant potentialof 0.10 V across the electrodes, and the current was recorded usingPSTrace software (v. 4.6) as the device was exposed to varyingconcentrations of analyte gas. For ammonia detection measurements, thechemiresistive device was enclosed in a PTFE chamber, and a gas mixersystem was used to deliver ammonia gas diluted by nitrogen. The gasmixer was comprised of two digital flow controllers purchased fromSierra Instruments. A MicroTrak Mass Flow Controller is used to deliverup to 4 mL/min of a mixture of 1% ammonia in nitrogen that was furtherdiluted in the gas mixer by nitrogen delivered by the other Mass FlowController at 2.00 L/min. Poly-4-vinylpyridine powder (P4VP, 2%cross-linked) was directly added to DECP (or DMCP) as a scavenger ofhydrochloric acid. DECP with P4VP was stirred with magnetic bar underdry N₂ flow for several days. Evaporation rate of DECP was calibratedbased on the decrease of mass. DECP vapor was diluted with dry N₂ tocreate DECP vapor with desired concentration (10, 1, 0.1 ppm).

Gas Detection Measurements (Wireless)

Conversion of a commercial NFC tag (RI-I11-114A-01, Texas Instruments)into a wireless chemical sensor was previously described. See,Azzarelli, J. M.; Mirica, K. A.; Ravnsbæk, J. B.; Swager, T. M. Proc.Natl. Acad. Sci. USA 2014, 111, 18162-18166, which is incorporated byreference in its entirety. Circuit design was further improved in thispaper for realizing smart phone turn-on and turn-off sensors. Thecircuit of an NFC tag was disrupted using a circular hole puncher (holediameter 2 mm; Bead Landing). A hole was punched through the tag,effectively removing a portion of the conducting aluminum film (alongwith the underlying polymeric substrate). The circuit was reconstructedvia electrically connecting interdigitated microelectrode(functionalized with SWCNT+MSP(Cu)) by silver glue to bridge the twodisconnected ends of aluminum. The reflection coefficient spectra werecollected with a network analyzer (Agilent E5061B). Smart phone (GalaxyS4, Samsung) was used for recognition of NFC tag at various positionsand distances. Saturated SOCl₂ vapor was diluted by 1200 times with air(relative humidity=16.2%, 17.1° C.), and the diluted vapor was used forsensing.

Scanning Tunneling Microscopy (STM) Measurement

An Agilent 5100 using constant current mode was used to perform all STMexperiments. A vibration isolation chamber was used to isolate the STMsetup from acoustic vibrations. Pt/Ir (80:20) wire was used tomechanically cut tips with a diameter of 0.25 mm. HOPG ZYB, NT-MDT wasused. Ortho-dichlorobenzene and 1-phenyloctane were purchased fromSigma-Aldrich. STM measurements were performed at the graphite/solutioninterface at room temperature. Fast scan direction is in the horizontaldirection of the image. The layers were relatively unstable, but wereable to be imaged at I_(set)=5 pA and V_(bias)=−700 mV. Sample for STMmeasurement was prepared as follows. AL (0.1 mg) dissolved in o-DCB(0.15 mL) was added with Cu(AcO)₂.H₂O solution in methanol (10.6 mM,16.4 μL, 1.0 molar equivalent for AL). The solution was sonicated for 1min, and then 1-phenyloctane (0.075 mL) was added. The solution wassonicated for 1 min, and then smoothly filtered by PTFE membrane (0.2μm). The clear green solution was used for STM measurement.

3.1 Synthesis of 2,6-Dimethoxy-9,10-dioctyl-anthracene (1a)

2,6-Dimethoxy-anthraquinone^(S1) (10.2 g, 38.0 mmol) in three neck roundbottom flask was vacuum dried and purged with dry argon, and added withdry THF (800 mL). The suspension was bubbled with dry argon for 10 min,and cooled to 0° C. by ice bath. Then, 2M n-C₈H₁₇MgBr in diethyl ether(100 mL, 200 mmol) was added with syringe. The resulting dark brownsolution was allowed to warm to room temperature, and stirred overnight.The reaction was quenched with saturated aqueous solution of NH₄Cl, andthe color of solution turned yellowish brown. THF was removed underreduced pressure. The precipitated solid was dissolved indichloromethane, and washed with 0.1 M HCl aq. Dichloromethane solutionwas dried over Na₂SO₄, and the filtrated solution was evaporated underreduced pressure. The resulting red brown solid was dried in vacuumovernight. The solid was dissolved in dry THF (300 mL), and the solutionwas added to the mixtures of SnCl₂.H₂O (22 g, 98 mmol) and acetic acid(300 mL) at room temperature. After 22 hr, the reaction was neutralizedwith 1% NaOH aq., and the product was extracted with hexane. The hexanesolution was dried over Na₂SO₄, and the filtrated solution wasevaporated to dryness. The crude product was purified with columnchromatography on silica gel using gradient of 0-20% of dichloromethanein hexane. The yellow and fluorescence compound was collected. Afterremoval of solvent under reduced pressure, the product wasrecrystallized from ethanol. Thus, 2,6-dimethoxy-9,10-dioctyl-anthracene(1a) was obtained as yellow needle crystal (1.0 g, 2.2 mmol, Yield:5.7%). ¹H-NMR (400 MHz, CDCl₃) in ppm: 8.14 (d, J=9.6 Hz, 2H, Ar—H),7.40 (d, J=2.6 Hz, 2H, Ar—H), 7.18 (dd, J=9.6, 2.6 Hz, 2H, Ar—H), 3.97(s, 6H, OCH₃), 3.45 (m, 4H, ArCH₂), 1.78 (m, 4H, CH₂), 1.56 (m, 4H,CH₂), 1.41 (m, 4H, CH₂), 1.28 (m, 12H, CH₂), 0.87 (t, 6H, CH₃). ¹³C-NMR(100 MHz, CDCl₃) in ppm: 156.2, 132.1, 129.2, 126.9, 126.7, 119.5,101.9, 55.3, 32.1, 31.0, 30.6, 29.8, 29.6, 28.7, 22.9, 14.3.HR-DART/FT-MS (m/z): calculated for [C₃₂H₄₆O₂+H]=463.3576 m/z, found463.3578 m/z. TLC: Rf=0.5 (dichloromethane:hexane=1:3).

3.2 Synthesis of 2,6-Dibromo-3,7-dimethoxy-9,10-dioctyl-anthracene (1b)

Selective bromination was performed according to literature procedure.See, Nakano, M.; Niimi, K.; Miyazaki, E.; Osaka, I.; Takimiya, K. Org.Lett. 2012, 77, 8099-8111., which is incorporated by reference in itsentirety. 1a (600 mg, 1.30 mmol) in three neck round bottom flask wasdried in vacuum, and purged with dry argon. Dry THF (60 mL) was added,and the solution was cooled down to 0° C. with ice bath. The solutionwas bubbled with dry argon for 10 min at 0° C. Then, 1.4 M sec-BuLi incyclohexane (5.1 mL, 7.1 mmol) was dropwisely added with syringe underargon atmosphere. The resulting dark green solution was stirred at 0° C.for 1 hr, and then 1,2-dibromotetrachloroethane (3.0 g, 9.2 mmol) wasadded quickly. The color of solution changed from dark green to yellow.The solution was allowed to warm to room temperature, and then furtherstirred for 2 hr. The reaction was quenched with saturated aqueoussolution of NH₄Cl. THF was removed under reduced pressure, and theresulting solid was washed with water and methanol on glass filter. Thesolid product (450 mg) was dried in vacuum. The crude produced was usedfor next step without further purification.

3.3 Synthesis of3,7-Dimethoxy-9,10-dioctyl-anthracene-2,6-dicarbaldehyde (1c)

The crude 1b (450 mg, 0.725 mmol if pure) in three neck round bottomflask was dried in vacuum, and purged with dry argon. Dry THF (88 mL)was added, and the solution was cooled to −78° C. The solution wasbubbled with dry argon for 10 min at −78° C. Then, 1.4 M sec-BuLi incyclohexane (4.4 mL, 6.2 mmol) was dropwisely added with syringe underargon atmosphere. The green solution was kept stirred at −78° C. for 30min, and then excess of dry dimethylformamide (5 mL) was addeddropwisely. The color of solution changed from green to yellow. Thesolution was allowed to warm to room temperature, and then furtherstirred for 1 hr. The reaction was quenched with water, and the solutionget orange. THF was removed under reduced pressure, and the resultingsolid was washed with water and methanol on glass filter. The orangesolid was purified by column chromatography on silica gel(dichloromethane:hexane=2:1). There are orange and pink bands on columnchromatography, and the pink band that comes out later from column wascollected. Solvent was removed under reduced pressure, and3,7-dimethoxy-9,10-dioctyl-anthracene-2,6-dicarbaldehyde (1c) wasobtained as a red solid (90 mg, 0.17 mmol, Yield: 13%). ¹H-NMR (400 MHz,CDCl₃) in ppm: 10.6 (s, 2H, CHO), 8.80 (s, 2H, Ar—H), 7.44 (s, 2H,Ar—H), 4.06 (s, 6H, OCH₃), 3.51 (m, 4H, ArCH₂), 1.78 (m, 4H, CH₂), 1.56(m, 4H, CH₂), 1.40 (m, 4H, CH₂), 1.27 (m, 12H, CH₂), 0.87 (t, 6H, CH₃).¹³C-NMR (100 MHz, CDCl₃) in ppm: 190.5, 155.6, 135.9, 131.4, 129.3,127.0, 126.8, 102.6, 55.6, 32.1, 31.4, 30.4, 29.7, 29.5, 28.7, 22.9,14.3. HR-DART/FT-MS (m/z): calculated for [C₃₄H₄₆O₄+H]=519.3474 m/z,found 519.3477 m/z. TLC: Rf=0.17 (dichloromethane:hexane=2:1).

3.4 Synthesis of3,7-Dihydroxy-9,10-dioctyl-anthracene-2,6-dicarbaldehyde (1d)

1c (70 mg, 0.13 mmol) in three neck round bottom flask was dried invacuum, and purged with dry argon. Dry dichloromethane (40 mL) wasadded, and the solution was cooled down to −78° C. The solution wasbubbled with dry argon for 10 min at −78° C. BBr₃ (0.5 mL) was dilutedwith dry dichloromethane (10 mL), and the BBr₃ (0.095 mL, 250 mg, 1.0mmol) in dry dichloromethane (2 mL) was dropwisely added to the solutionof 1c at −78° C. under dry argon. The resulting red brown solution waskept stirred at −78° C. for 1 hr, and the solution was allowed to warmto room temperature, and then further stirred overnight in dark. Thesolution was cooled to 0° C., and then the reaction was carefullyquenched with water. The solvent was removed under reduced pressure, andthe resulting solid was washed with water and methanol on glass filter.The solid was dissolved in acetone, and the removal of solvent underreduced pressure provided 1d (50 mg, 0.10 mmol, Yield: 77%). Due to thepossible instability of 1d in air, the product was used for next stepimmediately after checking NMR spectrum. ¹H-NMR (400 MHz, CDCl₃) in ppm:10.2 (s, 2H, OH), 9.97 (s, 2H, CHO), 8.60 (s, 2H, Ar—H), 7.62 (s, 2H,Ar—H), 3.47 (m, 4H, ArCH₂), 1.77 (m, 4H, CH₂), 1.53 (m, 4H, CH₂), 1.39(m, 4H, CH₂), 1.27 (m, 12H, CH₂), 0.87 (t, 6H, CH₃). ¹³C-NMR (100 MHz,CDCl₃) in ppm: 197.0, 153.1, 137.5, 135.9, 131.6, 127.5, 124.5, 108.6,32.1, 31.7, 30.5, 29.8, 29.5, 29.1, 22.9, 14.3.

3.5 Synthesis of9,10-Dioctyl-3,7-bis-propyliminomethyl-anthracene-2,6-diol (AL)

1d (25 mg, 0.051 mmol) in round bottom flask was dried in vacuum, andpurged with dry argon. Dry dichloromethane (20 mL) was added, and thesolution was added with n-propylamine (100 mg, 1.7 mmol) and anhydrousMgSO₄ (ca. 100 mg) at room temperature. The mixed solution was stirredfor 1 hr under dry argon, and then the MgSO₄ was removed by filtration.Solvent was removed under reduced pressure, and the resulting pink solidwas purified by gel permeation chromatography (BIO-RAD, Bio-Beads S-X1)using dichloromethane as eluent. The pink band was collected, and thensolvent was removed under reduced pressure. The pink solid was washedwith methanol on glass filter, and then the solid was dissolved indichloromethane. Removal of solvent under reduced pressure provided ALas a pink solid (20 mg, 0.035 mmol, Yield: 68%). Note that AL in solidstate was stable in air, while AL in CDCl₃ gradually provides impurity¹H-NMR signals when left in air over a week. ¹H-NMR (400 MHz, CDCl₃) inppm: 12.8 (s, 2H, OH), 8.58 (s, 2H, CH═N or Ar—H), 8.18 (s, 2H, CH═N orAr—H), 7.56 (s, 2H, CH═N or Ar—H), 3.65 (t, 4H, NCH₂), 3.43 (m, 4H,ArCH₂), 1.78 (m, 8H, CH₂), 1.56 (m, 4H, CH₂), 1.38-1.28 (m, 16H, CH₂),1.02 (t, 6H, CH₃), 0.87 (t, 6H, CH₃). ¹³C-NMR (100 MHz, CDCl₃) in ppm:165.0, 154.6, 133.0, 131.1, 129.7, 126.5, 122.9, 107.1, 62.2, 32.2,31.4, 30.6, 29.8, 29.6, 28.9, 24.3, 22.9, 14.3, 12.0. HR-ESI/FT-MS(m/z): calculated for [C₃₈H₅₆N₂O₂+H]=573.4415 m/z, found 573.4419 m/z.TLC: decomposed.

3.6 Synthesis of3,7-Dihydroxy-9,10-dioctyl-anthracene-2,6-dicarbaldehyde dioxime (ALOx)

AL in round bottom flask was dried in vacuum, and purged with dry argon.Dichloromethane (5 mL), methanol (1 mL), and water (ca. 0.05 mL) wereadded, and the solution was added with a few drops of trifluoroaceticacid. The mixture was stirred in argon overnight, and the color ofsolution turns to deep purple. Organic solvents were removed underreduced pressure, and the resulting solid was washed with water andmethanol on glass filter. The solid was dissolved in dichloromethane,and dried in vacuum. Complete hydrolysis of imine group was confirmed by¹H-NMR spectrum, and the product is identical to 1d. The solid wasdissolved in dry dichloromethane (3 mL) and ethanol (3 mL), and thesolution was added with hydroxylamine hydrochloride (150 mg). Themixture was stirred under argon for 3 hr, and then the color of solutionturned to orange. Solvents were removed under reduced pressure, and theresulting orange solid was washed with water and methanol. The productwas dissolved in acetone, and the removal of solvent under reducedpressure provided ALOx as an orange solid (3.0 mg, 0.0058 mmol, Yield:66%). ¹H-NMR (400 MHz, CDCl₃ and CD₃COCD₃) in ppm: 10.40 (s, 1.3H, OH,disappeared when CD₃OD added), 9.78 (s, 2H, OH, disappeared when CD₃ODadded), 8.42 (s, 2H, CH═N or Ar—H), 8.06 (s, 2H, CH═N or Ar—H), 7.51 (s,2H, CH═N or Ar—H), 3.36 (m, 4H, ArCH₂), 1.68 (m, 4H, CH₂), 1.50 (m, 4H,CH₂), 1.22 (m, 4H, CH₂), 1.22 (m, 12H, CH₂), 0.81 (t, 6H, CH₃). ¹³C-NMR(100 MHz, CD₃COCD₃) in ppm: 153.3, 153.1, 133.3, 130.4, 130.1, 127.4,122.2, 107.4, 32.7, 32.1, 23.4, 14.4. HR-ESI/FT-MS (m/z): calculated for[C₃₂H₄₄N₂O₄+H]=521.3379 m/z, found 521.3367 m/z.

3.7 Synthesis of Poly-(9,9-Di-(2′-ethylhexyl)-2,7-dibromofluorene)

Polymer was prepared by Ni(0)-catalyzed cross-coupling polymerization of9,9-Di-(2′-ethylhexyl)-2,7-dibromofluorene using modified procedure ofreported method. See, Yang, Y.; Pei, Q.; Heeger, A. J. J. Appl. Phys.1996, 74, 934-939, which is incorporated by reference in its entirety.NiCl₂ (8.2 mg, 0.063 mmol), PPh₃ (140 mg, 0.53 mmol), zinc dust (658 mg,10.1 mmol), 2,2′-bipyridine (9.0 mg, 0.058 mmol),9,9-di-(2′-ethylhexyl)-2,7-dibromofluorene (551 mg, 1.00 mmol) wereplaced in Schlenk flask, and dried in vacuum for 1 hr. Ar was purgedinto the flask, and degassed toluene (2 mL) and DMF (1 mL) were added.The mixture was stirred at 80° C. After 3 hr the mixture was poured intomethanol (50 mL), and the resulting white precipitate was washed withmethanol. The solid was dissolved in dichloromethane, and zinc powderwas removed using 0.2 μm PTFE membrane. The clear solution wasprecipitated into acetone, and white solid was collected on glassfilter. The white solid was dissolved in dichloromethane. Removal ofsolvent under reduced pressure providedpoly-(9,9-Di-(2′-ethylhexyl)-2,7-dibromofluorene) as a light white solid(180 mg, Yield: 46%). GPC (THF, polystyrene standard, RI detection):M_(n)=9.0 k, M_(w)=11.3 k, M_(w)/M_(n)=1.26.

Other embodiments are within the scope of the following claims.

What is claimed is:
 1. A system for detecting an analyte comprising: adetector; and a radio frequency identification tag including a sensorportion, the sensor portion configured to change resistivity when theradio frequency identification tag contacts or interacts with ananalyte, whereby the resistivity change alters an output of the radiofrequency identification tag, wherein the sensor portion includes acircuit, and wherein the sensor portion is configured to activate thecircuit or deactivate the circuit when contacted or having interactedwith the analyte, wherein the circuit includes a conductive materialassociated with a chemically-degradable polymer; the polymer including aligand and a metal ion.
 2. The system of claim 1, wherein the detectoris a reader.
 3. The system of claim 2, wherein the reader is a hand heldreader.
 4. The system of claim 3, wherein a hand held reader is asmartphone.
 5. The system of claim 4, wherein the tag becomes readablefrom unreadable to the detector after the conductivity changes.
 6. Thesystem of claim 4, wherein the tag becomes unreadable from readable tothe detector after the conductivity changes.
 7. The system of claim 1,wherein the system includes a dosimeter.
 8. The system of claim 7,wherein the dosimeter is a radiation dosimeter, a chemical warfare agentdosimeter, a volatile organic compound dosimeter, or an analytedosimeter.
 9. The system of claim 1, wherein the system monitors apollutant, a chemical relevant to occupational safety, a nerve agent, ora pulmonary agent.
 10. The system of claim 1, wherein the systemincludes a plurality of tags.
 11. The system of claim 10, wherein eachof the plurality of tags is capable of detecting at least one analyte.